This invention relates to a method of chlorinating and brominating aromatic compounds. In particular, it relates to a method of chlorinating and brominating aromatic compounds using a catalytic amount of a Lewis acid catalyst and about 0.001 to about 0.1 equivalents of an iodine cocatalyst at atmospheric pressure.
Aromatic compounds, such as methyl-4-methylbenzoate (M4MB), are commonly chlorinated at atmospheric pressure using chlorine gas in the presence of a Lewis acid catalyst, such as aluminum chloride, AlCl.sub.3, or ferric chloride, FeCl.sub.3. The amount of Lewis acid catalyst used must be greater than stoichiometric to effect the chlorination. For example, 0.98 lbs. (1.1 equivalents) of aluminum chloride are required to chlorinate each pound of M4MB.
If a weak Lewis acid is used, such as FeCl.sub.3, chlorination will stop after the addition of one chlorine atom. If further chlorination is desired, more vigorous conditions, such as a higher temperature and/or pressure, are required. These conditions tend to lead to decomposition and the formation of undesired side products.
After the reaction is complete, separation of the catalyst from the product by filtration or distillation is impractical or not possible because the catalyst is chemically bound to the product. The usual procedure is to add water, causing the catalyst to react with the water to form a soluble product. For example, an aluminum chloride catalyst reacts with water to form hydrochloric acid and aluminum hydroxide, which dissolve in the water and can be separated from the solid product.